High verticality InP/InGaAsP etching in Cl2/H2/Ar inductively coupled plasma for photonic integrated circuits

High verticality and reduced sidewall deterioration of InP/InGaAsP in Cl2/H2/Ar inductively coupled plasma etching is demonstrated for a hydrogen dominant gas mixture. Selectivity >20:1⁠, an etch rate of 24 nm/s, and a sidewall slope angle of >89° have been measured for etch depths >7 μm⁠. The Ar flow is minimized to reduce surface etch damage while increased Cl2 and H2 gas flow is shown to increase etch rate and selectivity. The high chamber pressure required for plasma ignition causes isotropic etching at the start and creates an undercut beneath the masking layer. A novel ignition scheme using a hydrogen gas “flood” is suggested and results are presented.